In recent years, it has been desirable that electronic devices such as servers or storages are densely implemented in a data center. On the other hand, the amount of heat generation of the electronic devices has increased with an increase in speed of the electronic devices.
In a case where electronic devices each having a large amount of heat generation are densely implemented, temperatures of the electronic devices exceed allowable upper-limit temperatures and cause an incorrect operation or a failure. Therefore, cooling methods each capable of fully cooling electronic devices each having a large amount of heat generation even in a case where the electronic devices are densely implemented are requested.
As one of such cooling methods, it is proposed that an electronic device is immersed in a liquid refrigerant and is cooled. Hereinafter, this type of cooling method will be called a liquid immersion cooling method. In the liquid immersion cooling method, an inactive liquid refrigerant having a high insulation property (a fluorocarbon compound, for example) is put into a liquid immersion tank, and an electronic device is immersed in the refrigerant, thereby circulating the refrigerant between the liquid immersion tank and a heat exchanger.
In the liquid immersion cooling method, it is proposed that an electronic device having a large amount of heat generation and an electronic device having a small amount of heat generation are immersed in refrigerants of respective different liquid immersion tanks (see, for example, Japanese Laid-open Patent Publication No. 5-160310 and so forth). Furthermore, it is proposed that a heat sink is attached to an element having a large amount of heat generation and the relevant heat sink is cooled by a dielectric coolant (see, for example, Japanese National Publication of International Patent Application No. 2011-518395 and so forth).
In general, in an information processing system, hard disks are used as external storage devices. Each of general hard disks is designed on the premise of being used in the atmosphere, and in a chassis thereof, vent holes for connecting between a space within the chassis and the outside thereof are provided. The reason is that an increase in pressure within the chassis, caused by heat generated along with an operation, is kept from deteriorating both a write characteristic and a read characteristic.
In a case where this type of hard disk is immersive in a refrigerant, the refrigerant enters the chassis from the vent holes, and surfaces of disks are covered by the refrigerant, thereby disabling reading and writing of data. Accordingly, it is difficult for this type of hard disk to be immersed in the refrigerant and to be used. This type of hard disk is an example of electronic components each having low liquid immersion resistance.
It is conceivable that, as a storage, a solid stare drive (SSD) or a hard disk filled with helium gas (hereinafter, called a He-filled hard disk drive (HDD)) is used. Since being hermetically sealed, the SSD and the He-filled HDD each have high liquid immersion resistance and are able to be immersed in the refrigerant and be used.
However, the SSD and the He-filled HDD have high production costs, compared with the above-mentioned general hard disks. Many storages are used in the data center. Therefore, in a case of using the SSDs or the He-filled HDDs, a construction cost of the information processing system is greatly elevated. In view of the above, it is desirable that, by using a liquid refrigerant, it is possible to cool an electronic component having low liquid immersion resistance in addition to an electronic component having high liquid immersion resistance.